1. Field of the Invention
The present invention relates to a brazing material which is used for brazing a metal member to another metal member of an electronic component such as a wiring board or a semiconductor device-housing package. More particularly, the present invention is concerned with a brazing material which is used to braze an outer lead terminal, heat sink, etc. to a metallized layer provided on a ceramic substrate.
2. Description of the Related Art
Conventional wiring boards with electronic components such as semiconductor devices, capacitors and resistors mounted or connected thereto are each constructed of a ceramic substrate composed of an aluminum oxide-based sinter, mullite-based sinter, silicon carbide-based sinter, aluminum nitride-based sinter or the like; a metallized wiring layer formed on the upper side of the ceramic substrate in a predetermined pattern, to which a semiconductor device, capacitor, etc. are electrically connected; and an outer lead terminal composed of an iron-nickel-cobalt alloy, iron-nickel alloy or the like which is attached to the metallized wiring layer via a brazing material to connect the metallized wiring layer to an external electric circuit, with a heat-sink member composed of a highly thermal-conductive material such as copper being attached to the underside of the ceramic substrate via a brazing material for satisfactory dissipation of heat generated by the semiconductor device, the resistor, etc. into the air.
Here, the heat-sink member is attached to the underside of the ceramic substrate by precoating the underside of the ceramic substrate with a backing metallized layer and brazing the member to the backing metallized layer via a brazing material.
The metallized wiring layer and the backing metallized layer to which the heat-sink member is brazed are composed of a high-melting metal such as tungsten, molybdenum or manganese, and are applied to the upper side or the underside of the ceramic substrate in a predetermined pattern by the well-known Mo-Mn method of the prior art.
A silver-copper alloy (silver brazing alloy) is usually used as the brazing material for brazing the outer lead terminal to the metallized wiring layer and as the brazing material for brazing the heat-sink member to the backing metallized layer.
Conventional semiconductor device-housing packages for housing semiconductor devices are each composed of a ceramic substrate with a semiconductor device-mounting portion (recessed portion) in the center of the upper side for mounting a semiconductor device; a metallized wiring layer which is formed as a coat extending from the periphery of the semiconductor-mounting portion to the perimeter of the upper side and leading out externally; a semiconductor device which is mounted in the semiconductor-mounting portion and is electrically connected to the metallized wiring layer (via a bonding wire, for example); an outer lead terminal which is attached to the outer end of the metallized wiring layer via a brazing material to connect the semiconductor device to an external electric circuit; and a lid bonded to the upper side of the ceramic substrate via a sealing material, with a heat-sink member which is composed of a highly thermal-conductive material such as copper and serves to satisfactorily dissipate heat generated by the semiconductor device into the air, being attached, via a brazing material, to the underside of the ceramic substrate, which are capable of housing the semiconductor devices in the inside.
Here, the heat-sink member is attached to the underside of the ceramic substrate by precoating the underside of the ceramic substrate with a backing metallized layer and brazing the member to the backing metallized layer via a brazing material.
The ceramic substrate, the outer lead terminal, the metallized wiring layer, the backing metallized layer, the heat-sink member, etc. of the semiconductor device-housing package are formed of the same or similar materials as those used for construction of the wiring board.
In the case of the semiconductor device-housing package as well, a silver-copper alloy (silver brazing alloy) is usually used as the brazing material for brazing the outer lead terminal to the metallized wiring layer and as the brazing material for brazing the heat-sink member to the backing metallized layer.
With the conventional wiring boards or semiconductor device-housing packages, however, when a silver-copper alloy (silver brazing alloy) is used as the brazing material for brazing the outer lead terminal to the metallized wiring layer or brazing the heat-sink member to the backing metallized layer applied to the underside of the ceramic substrate, since the silver-copper alloy has a fusing point as high as 780.degree. C., increased temperatures of the brazing material cause great variation in the degrees of thermal expansion of the ceramic substrate and the heat-sink member and of the ceramic substrate and the outer lead terminal, and this has presented drawbacks in that the ceramic substrate becomes cracked or impaired otherwise, the heat-sink member and the outer lead terminal peel off from the ceramic substrate thus preventing establishment of electric connection between the metallized wiring layer and the external electric circuit, the ceramic substrate is severely bent, and thus the semiconductor device, the capacitor, the resistor, etc. cannot be connected to the metallized wiring layer on the upper side of the ceramic substrate in a firm and precise manner.